A transistor pulls the output firmly high, and another transistor pull output firmly low.
Analog technology refers to electronic transmission accomplished by adding signals of varying frequency or amplitude to carrier waves of a given frequency of alternating electromagnetic current. Broadcast and phone transmission have conventionally used analog technology. Analog also connotes any fluctuating, evolving, or continually changing process. Analog is usually represented as a series of sine waves. The term originated because the modulation of the carrier wave is analogous to the fluctuations of the voice itself. A modem is used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer.
ADC (analog-to-digital conversion) Analog-to-digital conversion is an electronic process in which a continuously variable (analog) signal is changed, without altering its essential content, into a multi-level (digital) signal. The input to an analog-to-digital converter (ADC) consists of a voltage that varies among a theoretically infinite number of values. Examples are sine waves, the waveforms representing human speech, and the signals from a conventional television camera. The output of the ADC, in contrast, has defined levels or states. The number of states is almost always a power of two -- that is, 2, 4, 8, 16, etc. The simplest digital signals have only two states, and are called binary. All whole numbers can be represented in binary form as strings of ones and zeros. Digital signals propagate more efficiently than analog signals, largely because digital impulses, which are well-defined and orderly, are easier for electronic circuits to distinguish from noise, which is chaotic. This is the chief advantage of digital modes in communications. Computers "talk" and "think" in terms of binary digital data; while a microprocessor can analyze analog data, it must be converted into digital form for the computer to make sense of it. A typical telephone modem makes use of an ADC to convert the incoming audio from a twisted-pair line into signals the computer can understand. In a digital signal processing (DSP) system, an ADC is required if the signal input is analog.
The term "Boolean," often encountered when doing searches on the Web, refers to a system of logical thought developed by the English mathematician and computer pioneer, George Boole (1815-64). In Boolean searching, an "and" operator between two words or other values (for example, "pear AND apple")means one is searching for documents containing both of the words or values, not just one of them. An "or" operator between two words or other values (for example, "pear OR apple") means one is searching for documents containing either of the words. In computer operation with binary values, Boolean logic can be used to describe electromagnetically charged memory locations or circuit states that are either charged (1 or true) or not charged (0 or false). The computer can use an AND gate or an OR gate operation to obtain a result that can be used for further processing. The following table shows the results from applying AND and OR operations to two compared states: 0 AND 0 = 0 1 AND 0 = 0 1 AND 1 = 1 0 OR 0 = 0 0 OR 1 = 1 1 OR 1 = 1 The Gates: BUF, NOT, OR, NOR, XOR, XNOR, AND, NAND. A BUF gate acts simply as a buffer. It accepts one input and does not change the value for the output. Its primary purpose is to simply supply an additional gate delay to the signal passing through. It can be represented by "Y=A", where A is the value of the input, and Y is the value of the output. A NOT gate acts opposite of the BUF; it negates the output. It can be represented by "Y=*A". An OR gate accepts two inputs and results in one output. If either of the inputs are true, then the output is true, otherwise the output is false. It can be represented by "Y=A+B", where B represents the second input. An AND gate accepts two inputs and results in one output. If either of the inputs is false, then the output is false, but if both inputs are true, then the output is true. In can be represented by "Y=AB". An XOR gate accepts two inputs and results in one output. It is only true if one of the inputs is true and the other is false. It can be represented by "Y=A^B". In the cases of NOR, NAND, and XNOR, they act just like their respective counterparts (OR, AND, and XOR) except the output is just the opposite. Think of a NOR as being an OR gate immediately followed by a NOT gate. The is also true for NAND and XNOR.
Bouncing is the tendency of any two metal contacts in an electronic device to generate multiple signals as the contacts close or open; debouncing is any kind of hardware device or software that ensures that only a single signal will be acted upon for a single opening or closing of a contact. When you press a key on your computer keyboard, you expect a single contact to be recorded by your computer. In fact, however, there is an initial contact, a slight bounce or lightening up of the contact, then another contact as the bounce ends, yet another bounce back, and so forth. A similar effect takes place when a switch made using a metal contact is opened. The usual solution is a debouncing device or software that ensures that only one digital signal can be registered within the space of a given time (usually milliseconds)
A capacitor is a passive electronic component that stores energy in the form of an electrostatic field. In its simplest form, a capacitor consists of two conducting plates separated by an insulating material called the dielectric. The capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the separation between the plates. Capacitance also depends on the dielectric constant of the substance separating the plates. The standard unit of capacitance is the farad, abbreviated F. This is a large unit; more common units are the microfarad, abbreviated µF (1 µF = 10-6 F) and the picofarad, abbreviated pF (1 pF = 10-12 F). Capacitors can be fabricated onto integrated circuit (IC) chips. They are commonly used in conjunction with transistors in dynamic RAM (also called D-RAM or DRAM). The capacitors help maintain the contents of memory. Because of their tiny physical size, these components have low capacitance. They must be recharged thousands of times per second or the DRAM will lose its data. Large capacitors are used in the power supplies of electronic equipment of all types, including computers and their peripherals. In these systems, the capacitors smooth out the rectified utility AC, providing pure, battery-like DC.
CMOS is the semiconductor technology used in the transistors that are manufactured into most of today's computer microchips. Semiconductors are made of silicon and germanium, materials which "sort of" conduct electricity, but not enthusiastically. Areas of these materials that are "doped" by adding impurities become full-scale conductors of either extra electrons with a negative charge (N-type transistors) or of positive charge carriers (P-type transistors). In CMOS technology, both kinds of transistors are used in a complementary way to form a current gate that forms an effective means of electrical control. CMOS transistors use almost no power when not needed. As the current direction changes more rapidly, however, the transistors become hot. This characteristic tends to limit the speed at which microprocessors can operate.
As opposed to sequential, output depends on present input, "no memory."
Current is a flow of electrical charge carriers, usually electrons or electron-deficient atoms. The common symbol for current is the uppercase letter I. The standard unit is the ampere, symbolized by A. One ampere of current represents one coulomb of electrical charge (6.24 x 1018 charge carriers) moving past a specific point in one second. Physicists consider current to flow from relatively positive points to relatively negative points; this is called conventional current or Franklin current. Electrons, the most common charge carriers, are negatively charged. They flow from relatively negative points to relatively positive points. Electric current can be either direct or alternating. Direct current (DC) flows in the same direction at all points in time, although the instantaneous magnitude of the current might vary. In an alternating current (AC), the flow of charge carriers reverses direction periodically. The number of complete AC cycles per second is the frequency, which is measured in hertz. An example of pure DC is the current produced by an electrochemical cell. The output of a power-supply rectifier, prior to filtering, is an example of pulsating DC. The output of common utility outlets is AC. Current per unit cross-sectional area is known as current density. It is expressed in amperes per square meter, amperes per square centimeter, or amperes per square millimeter. Current density can also be expressed in amperes per circular mil. In general, the greater the current in a conductor, the higher the current density. However, in some situations, current density varies in different parts of an electrical conductor. A classic example is the so-called skin effect, in which current density is high near the outer surface of a conductor, and low near the center. This effect occurs with alternating currents at high frequencies. Another example is the current inside an active electronic component such as a field-effect transistor (FET). An electric current always produces a magnetic field. The stronger the current, the more intense the magnetic field. A pulsating DC, or an AC, characteristically produces an electromagnetic (EM) field. This is the principle by which wireless signal propagation occurs.
Digital describes electronic technology that generates, stores, and processes data in terms of two states: positive and non-positive. Positive is expressed or represented by the number 1 and non-positive by the number 0. Thus, data transmitted or stored with digital technology is expressed as a string of 0's and 1's. Each of these state digits is referred to as a bit (and a string of bits that a computer can address individually as a group is a byte). Prior to digital technology, electronic transmission was limited to analog technology, which conveys data as electronic signals of varying frequency or amplitude that are added to carrier waves of a given frequency. Broadcast and phone transmission has conventionally used analog technology. Digital technology is primarily used with new physical communications media, such as satellite and fiber optic transmission. A modem is used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer.
A logical theorem which states that the complement of a conjunction is the disjunction of the complements or vice versa. In symbols: not (x and y) = (not x) or (not y) not (x or y) = (not x) and (not y) E.g. if it is not the case that I am tall and thin then I am either short or fat (or both). The theorem can be extended to combinations of more than two terms in the obvious way. The same laws also apply to sets, replacing logical complement with set complement, conjunction ("and") with set intersection, and disjunction ("or") with set union. A (C) programmer might use this to re-write if (!foo && !bar) ... as if (!(foo || bar)) ... DeMorgan's theorems are extremely useful in simplifying expressions in which a product or sum of variables is inverted. The two theorems are: (16) (x+y)' = x' * y' (17) (x*y)' = x' + y' Theorem (16) says that when the OR sum of two variables is inverted, this is the same as inverting each variable individually and then ANDing these inverted variables. Theorem (17) says that when the AND product of two variables is inverted, this is the same as inverting each variable individually and then ORing them.
One of the more interesting things that you can do with Boolean gates is to create memory with them. If you arrange the gates correctly, they will remember an input value. This simple concept is the basis of RAM (Random Access Memory) in computers, and also makes it possible to create a wide variety of other useful circuits. Memory relies on a concept called feedback. That is, the output of a gate is fed back into the input. The simplest possible feedback circuit using 2 inverters. If you follow the feedback path, you can see that if Q happens to be 1, it will always be 1. If it happens to be 0, it will always be 0. Since it's nice to be able to control the circuits we create this one doesn't have much use, but it does let you see how feedback works. It turns out that in "real" circuits you can actually use this sort of simple inverter feedback approach. A more useful feedback circuit using 2 NAND gates. This circuit has 2 inputs (R and S) and 2 outputs (Q and Q'). Because of the feedback, it's logic table is a little unusual compared to the ones we have seen previously: R S Q Q' 0 0 Illegal 0 1 1 0 1 0 0 1 1 1 Remembers What the logic table shows is that, if R and S are opposites of one another, Q follows S and Q' is the inverse of Q. If both R and S are switched to 1 simultaneously, then the circuit remembers what was previously presented on R and S. There is also the funny "illegal" state. In this state R and S both go to 1, which has no value in the memory sense. When Reset is applied, Q = 0, Qbar = 1, when Set is applied, Q = 1, Qbar = 0.
Same as a PAL (plus iterative stuff --ignore), but the output wires can be (statically) inverted or not inverted; PALs' outputs are always inverted. This provides more flexiblity in implementing EITHER POS's or SOP's.
A conductive body used as a return for electric currents and as an arbitrary zero of potential.
An integrated circuit (IC), sometimes called a chip or microchip, is a semiconductor wafer on which thousands or millions of tiny resistors, capacitors, and transistors are fabricated. An IC can function as an amplifier, oscillator, timer, counter, computer memory, or microprocessor. A particular IC is categorized as either linear (analog) or digital, depending on its intended application. Linear ICs have continuously variable output (theoretically capable of attaining an infinite number of states) that depends on the input signal level. As the term implies, the output signal level is a linear function of the input signal level. Ideally, when the instantaneous output is graphed against the instantaneous input, the plot appears as a straight line. Linear ICs are used as audio-frequency (AF) and radio-frequency (RF)amplifiers. The operational amplifier(op amp) is a common device in these applications. Digital ICs operate at only a few defined levels or states, rather than over a continuous range of signal amplitudes. These devices are used in computers, computer networks, modems, and frequency counters. Logic gates are the fundamental building blocks of digital ICs that work with binary data, that is, signals that have only two different states, called low (logic 0) and high (logic 1).
A Mosfet belongs to the FET family of transistors. A FET is a Field-Effect Transistor also known as a unipolar transistor because the current is conducted by only one type of carrier (electrons or holes) depending on the type of FET (n channel or p channel). Since the late 1970s, a particular kind of FET, the Metal-Oxide Semiconductor Field-Effect Transistor or MOSFET, has become extremely popular. Compared to BJTs (Bipolar Junction Transistors), MOS transistors can be made quite small (that is, occupying a small silicon area on the IC ship), and their manufacturing process is relatively simple. Furthermore, digital logic and memory functions can be implemented with circuits that exclusively use MOSFETs (that is, no resistors or dieodes are needed). For these reasons, most very-large-scale integrated (VLSI) circuits are made at the present time using MOS technology. Examples include microprocessor and memory chips.
Multiplexing is sending multiple signals or streams of information on a carrier at the same time in the form of a single, complex signal and then recovering the separate signals at the receiving end. Analog signals are commonly multiplexed using frequency-division multiplexing (FDM), in which the carrier bandwidth is divided into subchannels of different frequency widths, each carrying a signal at the same time in parallel. Digital signals are commonly multiplexed using time-division multiplexing (TDM), in which the multiple signals are carried over the same channel in alternating time slots. In some optical fiber networks, multiple signals are carried together as separate wavelengths of light in a multiplexed signal using dense wavelength-division multiplexing (DWDM).
Short for negative-channel metal-oxide semiconductor, and pronounced en-moss, a type of semiconductor that is negatively charges so that transistors are turned on or off by the movement of electrons. In contrast, PMOS (positive-channel MOS) works by moving electron vacancies. NMOS is faster than PMOS, but also more expensive to produce.
Disturbance in a signal
Ohm's Law is the mathematical relationship among electric current, resistance, and voltage. The principle is named after the German scientist Georg Simon Ohm. In direct-current (DC) circuits, Ohm's Law is simple and linear. Suppose a resistance having a value of R ohms carries a current of I amperes. Then the voltage across the resistor is equal to the product IR. There are two corollaries. If a DC power source providing E volts is placed across a resistance of R ohms, then the current through the resistance is equal to E/R amperes. Also, in a DC circuit, if E volts appear across a component that carries I amperes, then the resistance of that component is equal to E/I ohms. Mathematically, Ohm's Law for DC circuits can be stated as three equations: E = IR I = E/R R = E/I When making calculations, compatible units must be used. If the units are other than ohms (for resistance), amperes (for current), and volts (for voltage), then unit conversions should be made before calculations are done. For example, kilohms should be converted to ohms, and microamperes should be converted to amperes.
Like a PLA, but has a FIXED OR array. This means that each output has its own p product terms to choose from (rather than a pool of p terms). A PAL16L8 allows 16 input variables (and their complements), 8 outputs, and up to 7 product terms per output. Each output also has an "output enable gate" which is turned on by a dedicated AND gate. Thus, each output may be programmed as always enabled, always disabled, or based on the result of some product of inputs. Outputs are active low. 18 pin IC is used, so 6 pins are bi-directional and function as 1) inputs ONLY, 2) outputs ONLY, or 3) output to start, and then cycle back into the circuit as a 2nd pass input.
Two level AND-OR device that may realize any sum-of-products expression, limited by # inputs (n), # outputs (m), and the # of product terms (p). Might refer to "an n x m PLA with p product terms." Thus, to program the device, you simply choose which inputs you want for each of the (up to) p product terms, then you choose which product terms go with which output. For a 1 output, leave one column of the AND array empty and attach it to the output. For 0 output, leave the output unconnected to any of the product terms. Programmable Logic Devices (PLD's) Combinational PLD's contain only combinational elements, no sequential ones. Comparing, adding, and and other "iterative" operations are usually poor candidates for PLD design.
Resistance is the opposition that a substance offers to the flow of electric current. It is represented by the uppercase letter R. The standard unit of resistance is the ohm, sometimes written out as a word, and sometimes symbolized by the uppercase Greek letter omega. When an electric current of one ampere passes through a component across which a potential difference (voltage) of one volt exists, then the resistance of that component is one ohm. In general, when the applied voltage is held constant, the current in a direct-current (DC) electrical circuit is inversely proportional to the resistance. If the resistance is doubled, the current is cut in half; if the resistance is halved, the current is doubled. This rule also holds true for most low-frequency alternating-current (AC) systems, such as household utility circuits. In some AC circuits, especially at high frequencies, the situation is more complex, because some components in these systems can store and release energy, as well as dissipating or converting it. The electrical resistance per unit length, area, or volume of a substance is known as resistivity. Resistivity figures are often specified for copper and aluminum wire, in ohms per kilometer. Opposition to AC, but not to DC, is a property known as reactance. In an AC circuit, the resistance and reactance combine vectorially to yield impedance.
ROM is "built-in" computer memory containing data that normally can only be read, not written to. ROM contains the programming that allows your computer to be "booted up" or regenerated each time you turn it on. Unlike a computer's random access memory (RAM), the data in ROM is not lost when the computer power is turned off. The ROM is sustained by a small long-life battery in your computer. If you ever do the hardware setup procedure with your computer, you effectively will be writing to ROM.
are quantities which are fully described by a magnitude alone.
An impulse or fluctuating electrical quantity, as voltage or current, whose variations represent coded information.
The transistor, invented by three scientists at the Bell Laboratories in 1947, rapidly replaced the vacuum tube as an electronic signal regulator. A transistor regulates current or voltage flow and acts as a switch or gate for electronic signals. A transistor consists of three layers of a semiconductor material, each capable of carrying a current. A semiconductor is a material such as germanium and silicon that conducts electricity in a "semi-enthusiastic" way. It's somewhere between a real conductor such as copper and an insulator (like the plastic wrapped around wires). The semiconductor material is given special properties by a chemical process called doping. The doping results in a material that either adds extra electrons to the material (which is then called N-type for the extra negative charge carriers) or creates "holes" in the material's crystal structure (which is then called P-type because it results in more positive charge carriers). The transistor's three-layer structure contains an N-type semiconductor layer sandwiched between P-type layers (a PNP configuration) or a P-type layer between N-type layers (an NPN configuration). As the current or voltage is changed in one of the outer semiconductor layers, it affects a larger current or voltage in the inner layer resulting in the opening or closing of an electronic gate. Today's computers use circuitry made with Complementary Metal Oxide Semiconductor (CMOS) technology. CMOS uses two complementary transistors per gate (one with N-type material; the other with P-type material). When one transistor is maintaining a logic state, it requires almost no power. Transistors are the basic elements in integrated circuits or ICs, which consist of very large numbers of transistors interconnected with circuitry and baked into a single silicon microchip or "chip."
Short for transistor-transistor logic, a common type of digital circuit in which the output is derived from two transistors. The first semiconductors using TTL were developed by Texas Instruments in 1965. The term is commonly used to describe any system based on digital circuitry, as in TTL monitor.
are quantities which are fully described by both a magnitude and a direction.
Voltage, also called electromotive force (EMF), is an expression for electric potential or potential difference. If a conductive or semiconductive path is provided between the two points having a relative potential difference, an electric current flows. The common symbol for voltage is the uppercase letter V or E. The standard unit is the volt, symbolized by V. One volt is the EMF required to drive one coulomb of electrical charge (6.24 x 1018 charge carriers) past a specific point in one second. Voltage can be either direct or alternating. A direct voltage maintains the same polarity at all times. In an alternating voltage, the polarity reverses direction periodically. The number of complete cycles per second is the frequency, which is measured in hertz. An example of pure direct voltage is the EMF between the terminals of an electrochemical cell. The output of a power-supply rectifier, prior to filtering, is an example of pulsating direct voltage. The voltage that appears at the terminals of common utility outlets is alternating. A potential difference produces an electrostatic field, even if no current flows. As the voltage increases between two points separated by a specific distance, the electrostatic field becomes more intense. As the separation increases between two points having a given potential difference, the electrostatic flux density diminishes in the region between them. A single charged object is surrounded by an electrostatic field whose intensity is directly proportional to the voltage of the object relative to other objects in its vicinity.